Audio response device with orthogonal scan of multiple tracks on playback

ABSTRACT

An audio response data storage system including a plurality of voice frequency range sound tracks of approximately one half second duration. The system employed uses an orthogonal scanning technique which obtains automatic multiplexing of all of the tracks for access over a very small period of time. Scanning speed is at approximately five times the real time readout rate, and the entire record is scanned in approximately one tenth of a second, whereby data from any selected track segment does not suffer more than a one tenth second cueing time delay, resulting in a complete absence of choppy timing and the obtaining of a good natural sounding speech when the device is used as a voice response generator.

United States Patent 1 91 1111 3,872,264

Cotter Mar. 18, 1975 AUDIO RESPONSE DEVICE WITH 3,674,922 7/1972 Salamanl78/DIG. 3 3,701,846 10/1972 Zenzefilis l78/DIG.3 ORTHOGONAL SCAN OFMULTIPLE 3,769,468 10/1973 Shutterly 179/1003 A TRACKS ON PLAYBACKMitchell A. Cotter, Riverdale, NY.

[73] Assignee: APM Corporation, Englewood, NJ.

[22] Filed: Nov. 1, 1972 [2]] App]. No.: 302,822

[75] Inventor:

Primary Examiner-Bernard Konick Assistant Examiner-Alan Faber Attorney,Agent, or Firm-Charles E. Temko [57] ABSTRACT An audio response datastorage system including a plurality of voice frequency range soundtracks of ap- [52] 179/1003 179/1003 ig fii proximately one half secondduration. The system em- {511 Int Cl Gllb 7/02 ployed uses an orthogonalscanning technique which ['58] Fie'ld A DIG q. obtains automaticmultiplexing of all of the tracks for 79/100 "A"" 6 access over a verysmall period of time. Scanning speed is at approximately five times thereal time readout rate, and the entire record is scanned in approxi-References uted mately one tenth of a second, whereby data from anyUNITED STATES PATENTS selected track segment does not suffer more than a2,644,857 7/1953 Pierre l79/l00.3 A one tenth second cueing time delay,resulting in 21 2,900,443 8/1959 Camras 179/1002 T complete absence ofchoppy timing and the btaining g fg of a good natural sounding speechwhen the device is 0 mar 3,383,462 /1968 Banning 179/1002 CR used as aresponse generator 3,585,293 6/1971 Crowder 178/67 A 3 Claims, 10Drawing Figures 22 c127 POWER 'EQQI 2/ PULSE LINE fi AMPLIFIER SUPDLYA/6 f TQANSVERSAL g 30 FILTER PT 7 2t? sYNC TRACK g S EP COMPARATOR PULSEDR m (S BET) COUNTER OUT-OPRANGE i 1 1 3/ I t 1 "1 "1 1 1 PWMDISCDIMINATOR 4 1 e INTEGRATOR it TlMING CHAIN & l i 1 3 TRACK SELECT 18BIT+SIGN 1 REGISTERS A/D 1 37 1 'L' -22 l REAL TIME 1 1 CONVERTER lBASE r CONTROL LOGIC CLOCK yo COMPUTOQ 1 t2 1 1 EXTERNAL i COMMANDSPATENTEU MAR] 1 75 SHLU 2 UP 6 A52 CONTROL COMPUTED r i STEERING ADDRESSMULTIDLEXER 1 TO CHANNEL GATES M TRACK UNT T CO STA E SEOTOD COUNT STATEHHHH m S cOM PARATOR SECTOR H COM PADATOR SECTQF? SELECT TRACK SELECTCOMMAND R EGISTER FATENTED 1 81975 3, 872.264

sum u ur g DATA OUT I 0f; 3r M AL BL $57 A READOUT A g DEALTIME CLOCKBSHIFT REG- w ASHIFT REG- DATA OUT ISTED SET ISTEIQ SET BDATA 'IN /Z? ABL A DATAIN LOAD CLOCK B A sYNcasECTom 54 L L 27 INHIBIT GATE C* BINDEXAINDEX A MEMORY C SUMMED DATA IN L CQNTQOL CONTROL J LOGIC DATA 8 BITDATA IN +SIGN R A/D .g DIGITAL ADDEQ CIONVEIIZTER SYNC a SECTOQ'I IINHIBIT GATE mmEm- 1 8% 3.872264 sums or 6 E DGE D E LAY 4COUNT 64-COUNT RESET ALL X 3 BIT 6 BIT AUDIO RESPONSE DEVICE WITH ORTHOGONAL SCANOFMULTIPLE TRACKS ON PLAYBACK This invention relates generally to thefield of data storage, and more particularly to the storage andretrieval of syntactical and phonemic data for audible reproduction.Reference is made to my co-pending application, filed jointly withBernard David Nadler, Ser.

No. 295,234, filed Oct. 5, 1972, now U.S Pat. No.

3,810,106, and entitled SYSTEM FOR STORING TONE PATTERNS FOR AUDIBLERETRIEVAL,

which discloses and claims related inventions. The

present disclosure relates to a relatively simpler device particularlyadapted for the reproduction of a stored spoken vocabulary.

BRIEF DESCRIPTION OF THE PRIOR ART In prior art devices, audible soundsare normally stored in parallel tracks upon rotating drums or othermoving storage mediums, and a separate pick up or other retrieval deviceis used for each track. Given consideration of space and cost, mostaudible retrieval devices in the prior art are limited to relativelysmall vocabularies of the order of less than 50 words, and seldomexceeding 100 words.

In the above mentioned co-pending application, which is assigned to thesame assignee as the instant application, there is disclosed a somewhatanalogous system particularly suited for the storage and retrieval ofmusical tone patterns. The device includes a generallyrectangularly-shaped storage record having a large plurality of recordedsound tracks of finite length arranged in parallel juxtaposed positionupon the record. The record is scanned orthogonally at very high speedin raster-like fashion such that each deflection of scanning beingprependicular to the axis of the sound tracks crosses all of the tracks,thus potentially reading all of the information contained in the recordto make the same available for retrieval over a very short period oftime. Scanning is performed using a laser beam, and electro-opticalreproduction is performed at a far greater rate than real time outputrates. Analog retrieval signals are converted to digital values, and arerapidly stored using one or more storage registers which are thenunloaded at relatively slower intervals, the retrieved signals thenbeing again converted to analog values, suitably modified, amplified,and transduced.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present disclosurerelates to an analogous system which can be manufactured atsubstantially lower cost using substantially less sophisticatedhardware, and is of value where the demands of the system aresubstantially less. In a speech retrieval device, normally a vocabularyof several hundred words is adequate, and if a greater vocabulary isrequired, it is possible to store the data in terms of phonemic andsyntactical elements, rather than in entire words. Since normal speechproceeds at a far slower rate than musical reproduction, expensive itemssuch as a laser beam scanner are not required, and pulse modulationparameters are well within the capability of simpler scanning equipment,such as cathode ray tubes and the like.

However, it is often desirable for a voice response system to havemultiple outputs independent of each other in order to supply multipleresponses with a single system. The present embodiment thereforeincludes timing and addressing means, including comparators whichproduce an output command for a sampling pulse to occur when the addressin a register loaded by the control logic agrees with the status of thetiming chain. This output command may be multiplexed to any number ofsamplers and related output circuits by yet another address delivered bythe control logic. The control logic orders the called channels into asequence in increasing order of channel position so that as the y scanprogresses it may steer the channel or track data to the correct outputby the address in the multiplexer. Each individual output requires itsown sampler gates, as well as a signal demodulator, digitizer and realtime converter. These elements may be, for the most part, inexpensivedigital hardware, and they readily lend themselves to furtherintegration to result in a very economic approach. The control timinglogic is common to all the outputs, and need not be expanded to handleall of a hundred channel outputs or more.

The lowered cost of manufacture is principally the result of slower scantime as well as less data and storage of the same. While the currentgates and digitizer are all able to operate at a faster speed thandisclosed, scan speed is determined by these and another feature of thesystem. The choice of number of tracks and the length of the recordtogether with the minimum sampling time determine the overall scan time.The number of data points multiplied by the minimum sample time equalsthe scan period. The minimum time in the disclosed system arises fromthe decay rate of the phosphor of the cathode ray tube scanner. Thefastest currently available phosphor decay is found in a thin layer(about 1 mg/cm of P 16 type CaMgSio zCe activated and quenched to speedup decay. This phosphor emits principally in the ultraviolet rangecentered at 380 nm. with about 5 percent efficiency. For very rapidscanning, the decay which is of the order of 50 to nanoseconds for 1/eof output becomes a limitation on the discrimination between twodistinct openings in the data record track. The attack time or build upof radiation is extremely fast, being less than a few nanoseconds. Inorder to enhance the detector response from the record, the tracksdiffer in configuration substantially from those of the above mentionedco-pending application. Each track has a sync or start gap in a periodicposition, and the modulation occurs by moving the position of a secondgap in relation to it. While the reference gaps are all in a periodicposition in space on the record, the scan may not be that precise thatthe modulation gap could be used alone against a precisely clocked startpulse. Without a great precision in the deflection of the scanner, thiscould not provide the low noise and accurate modulation of the scannedsample light pulse position. The reference gap is used to control thedeflection sweep by locking it to the clock system through positionfeedback by comparing the reference pulses with the clock. The lightpulses are then able to operate a pulse width or position discriminator.Because of the slow decay of the phosphor, a transversal filter is usedto differentiate the light output of the photodetector by providingpulses coincident with the rising edges of the gaps as represented bythe sampling light pulses. The minimum gap spacing chosen (50 microns)represents for the scanning rates selected. a pulse to pulse time ofonly just under 10 nanoseconds. Without a transversal filter the systemwould not function, and with a practical version of the filter, the scanrate disclosed is approximately the maximum. The photodetector chosendoes not contribute to the response speed limits, as it is so muchfaster and in this respect, the use of the filter is relativelydifferent from that disclosed in the above mentioned application.

In order to obtain a sufficient number of photons into the photodetectorat acceptably low electron beam currents, it is necessary to use a fiberoptic cathode ray tube faceplate. High beam currents tend to burn thephosphor screen and limit operating life. Using a lightly alumiriizedscreen (about 100 nm) the fiber optic faceplate increases light outputover that from solid faceplates by more than 20 times. The glass fibersare chosen for good near ultraviolet transmission, and are microns orsmaller in diameter. To prevent scatter and loss of resolution andradiant energy level, the faceplate and the data record plate aremounted with an immersion oil fluid filling the glass to glass air gap.The oil has an index of refraction approximately the same as the glassfaceplate and glass record. The collimated radiant energy from thefibers is therefore undivergent in its passage into and through the datarecord plate. Once through, the energy is collected by a lens and aphotodetector system.

The modulation is of pulse width modulation type, and as compared withthe disclosure in the above mentioned co-pending application, emittercoupled logic is adequate since the speed of tunnel diodes isunnecessary. The modulation pulse position moves plus or minus 75ns. for100 percent modulation. The modulation provides 40 to 50 db of signal tonoise ratio, and does not vary with the aging of the cathode ray tube orthe word selection position. The noise is sensitive to scan ratechanges, but the disclosed deflection feedback system serves to lock thesweep smoothly to the record tracks, and thereby to the timing chain. Itis important in the disclosed system that the sweep not have anysignificant noise modulating its sweep speed across a single track (highfrequency type) of from slice to slice and so on as the scan progressesdown the track which would produce frequency noise. The locking actionprovides correction for both types of noise.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, to which referencewill be made in the specification, similar reference characters havebeen employed to designate corresponding parts throughout the severalviews.

FIG. 1 is a schematic block diagram of an embodiment of the invention.

FIG. 2 is a schematic side elevational view of the cathode ray tubescanner interconnected to the data record plate forming a part of theembodiment.

FIG. 3 is a view in elevation of the data record plate.

FIG. 4 is a fragmentary enlarged view of the data record platecorresponding to the upper left hand portion of FIG. 3.

FIG. 5 is a much enlarged fragmentary view of the data record plateshowing adjacent segments of two data tracks.

FIG. 6 is a schematic elevational view of the data record plate showingthe progressive vertical scan.

FIG. 7 is a block diagram showing the operation of alternately storedand unloaded data output registers.

FIG. 8 is a block diagram showing Y scan clocking.

FIG. 9 is a block diagram showing X scan clocking.

FIG. 10 is a block diagram showing address means used in conjunctionwith multiple output channels.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT In accordance with theinvention, the device, generally indicated by reference character 10,comprises broadly: (see FIG. 1) a control logic computer 11, serviced byan external command interface 12, and having a control link 13 to atiming chain and track select register module 14. The last mentionedmodule controls a sweep drive 15 controlling a power supply 16 and yoke17 of a cathode ray tube scanner 18. The scanner 18 scans a data recordplate 19 and interposed between it and a photo detector 20 and storingwords or phenemes. The output of the detector 20 flows through atransversal filter 21 to a pulse line amplifier 22 feeding a data bussto be sampled 23 supplying auxiliary output systems 24, 25 and 26. Theamplifier 22 also feeds a track pulse counter 27 feeding a synccomparator 28. A link 29 interconnects the comparator 28 to the sweepdrive 15, and a second link 30 interconnects it to an out-of-rangeindicator 31. The timing chain module 14 includes a link 32 to a crystalcontrolled base clock having a base frequency of 9.398160 Megahertz.Another link 33 interconnects to a data AND gate 34, the output of whichis fed to a pulse width modulation discriminator and integrator 35. Theoutput of the integratoris to an 8 bit-plus-sign analog-to-digitalconvertor 36 in turn, feeding a link 37 to a real time convertor 38having digital to analog output. This output is controlled by a link 39to a low pass filter 40 and thence to an amplifier 41 and audio output42.

The control logic computer 11 may be of conventional type, responding toone or more commands serially introduced, in response to which thecomputer unblanks selected portions of the data record plate 19 for thecorresponding data. As will more fully appear hereinafter, the computercan service a plurality of demands, responding in the order in which thecorresponding data is reached as part of a continuous scanningoperation. The information can be gated to separate outputs as a resultof an address command. A typical example, would be a telephonesubscriber service for stock market quotations, in which the output ofthe system is interfaced to a telephone switchboard mechamsm.

The cathode ray tube scanning system 18 employs several known elementsin a novel operative combination. The tube 48 includes a five inchsquare face formed by a ground fiber-optic faceplate 49 which serves tocollimate the output of the scanning beam along an axis parallel to theprincipal axis of the tube. The faceplate 49 is surrounded by an oilseal 51 which entraps an immersion oil film 52 filling the intersticebetween the faceplate 49 and a surface of the data record plate 19.Energy emanating from the plate 19 passes through a focusing lens system52 to fall upon a (5 1 than 3H2. Referring to FIGS. 3 to 6. inclusive.the data record plate 19 is in the form ofa 5 inch X 7 inch metalcladplate, microflat grade 2, 0.250 inches thick (Eastman Kodak Company).The metal-clad surface faces the scanner. It is bounded by an upper edge57, a lower edge 58, and side edges 59 and 60. The recorded area 61 is4.282 inches square and is divided into five sectors 62, 63, 64, 65 and66. The first sector 62 is bounded by a start sync band 67 of width0.06304 inches (64 X microns). Each sector is 0.806715 inches in width(819 X 25 microns). The sector sync bands 68, 69, 70, 71 and 72 are each0.03152 inches (32 X 25 microns).

As best seen in FIGS. 4 and 5, the horizontally recorded tracks 73 areof a total width of 550 microns, including a micron clear band 74. Themodulated portion of the track 75 is also 30 microns wide, so that theopaque metal film of the plate is open only in the 30 micron areas 74and 75, for reasons which will become more fully apparent hereinafter.

Referring to FIG. 6, the scan pattern starts with an oversweep of thetop edge 77 of the recorded area near the dot 78 and proceeds top tobottom, with the y sync proceeding from left to right. There are 819scanning slices in each sector, with each sector sync ba'nd being 32slices wide.

FIGS. 8 and 9 disclose the y sweep clocking and x sweep clocking,respectively. Pulses from t the base clock 80 pass through a two to onedivider supplying pulses of 9.39816 Megahertz frequency to an AND gate82 to a 4 bit counter 83, the output of which feeds an OR gate 84. Theoutput of the gate 84 is fed to an AND gate 85 which gates the start ofthe y sweep and unblanking of the scanner. A link 86 feeds a link 87 toan AND gate 88 to an 8 bit counter 89 which counts the 200 horizontaltracks as they are orthogonally scanned. At the completion of eachslice, a signal from an invertor 90 inhibits the gate 88, and the samesignal starts the retrace for they sweep. This signal sets an AND gate91 to a 4 bit counter 92 which counts the 8 intervals constituting theend sync period, the counter then resetting the y sweep at 93, andproviding a 43.51 kHz pulse train at 95 to the x sweep clocking, wherebythe x sync moves rightwardly as seen in FIG. 4 for the next slice. Thepulse 95 feeds an AND gate 96 feeding a 6 bit counter 97 which countsthe 64 intervals corresponding to the start sync band, and then throughan invertor 98, the gate 96 is inhibited, and the same output is linkedat 101 to enable an AND gate 102 gating to a 10 bit counter 103 whichcounts the 819 sweep slices of each sector. The output of the counter103 is inverted at 104 to inhibit the gate 102, and also through link105 to enable AND gate 106 which gates to a 5 bit counter 107 whichcounts the 32 slices constituting each sector sync. The output of thecounter 107 passes to an invertor 108 which inhibits the gate 106, andoperates a one shot multivibrator 109. The multivibrator 109 enables anOR gate 111 which resets the counter 103 through link 114, and counter107 through an edge delay line 112 and link 113. The multivibrator 109also feeds a three hit counter 115 of four count capacity to gate an ANDgate 116 which feeds a 6 bit counter 117 which counts the 64 intervalsin the end sync band 76 at the rightward end of the x sweep excursion.The output of the counter 117 resets at 118 all of the x sweepfunctions, and a pulse along the link 120 starts the re trace of the xsweep and blanks the cathode ray tube scanner. The x sweep is started bya 42.51 kHz pulse 95 to an AND gate 100, in conjunction with a pulsefrom an OR gate 99 gated by the counter 97.

Referring again to FIG. 5, in order to enhance the detector responsefrom the record, the track pattern is substantially different from thatdisclosed in the above mentioned co-pending application. In the presentembodiment, each track has a sync or start gap in a periodic position,and the modulation occurs by moving the position of a second gap inrelation to it. While the reference gaps are all in a periodic positionin space on the record, the scan may not be that precise that themodulation gap could be used alone against a precisely clocked startpulse. Without a great precision in the deflection of the scanner thiscould not provide the low noise and accurate modulation of the scannedsample light pulse position. The reference gap is used to control thedeflection sweep by locking it to the clock system through positionfeedback by comparing the reference pulses with the clock. The lightpulses are then able to operate a pulse width or position discriminatorsimilar in action to that used in the above mentioned application.Because of the slow decay of the phosphor, a transversal filter is usedto differentiate the light output of the photodetector providing pulsescoincident with the rising edges of the gaps as represented by thesampling light pulses. The minimum gap spacing chosen (50 microns)represents for the scanning rates selected, a time separation of onlyjust under 10 nanoseconds. Thus, without a transversal filter, thesystem would be inoperable, and with a practical version of the filter,the scan rate is at approximately maximum. It may be observed that thephotodetector chosen does not contribute to the response speed limits,as it is capable of much faster operation, and in this regard, the useof the filter is substantially different from that disclosed in theabove mentioned co-pending application. The sync comparator 28 (FIG. 1)which receives signals both the photodetector and the timing chainmodule 14 performs the above described function.

FIG. 7 illustrates the real time convertor 38 in greater 8 detail. Thefunction of this structure is to enable digital information toalternately flow into one or another of two memory register sets, sothat one may be loaded, while the other is unloaded to create acontinuous flow of digital information, which is subsequently convertedback to analog data. Each set of shift registers is loaded with datafrom the analog to digital converter which passes through an 8 bit plussign digital adder 125. This adder permits the addition of laterselected track segments to be added to the segments previously sampledwithout loss or disturbance of data. The memory shift register set thusis unloading the just previously loaded sector data during eachsubsequent sector scan. The adder accomplishes thesimple addition oflater selected data permitting the coincident reproduction of data fromany sectors. After five such loading cycles, the shift register set istransferred durng the synchronizing interval from load operation atsampling rate to unload operate at real time clock rate by the AND gates126 and 127 to the registers 128 and 129, in cooperation with load clock129 which controls gates 130 and 131, and readout gates 132 and 133controlled by real time clock 134. Each of the parallel registers inboth A and B sets are 819 bits long. The load clock is synchronized tothe fast scan. Unloading, however, is 5 5/16 times slower and iscontrolled by the readout clock 134 operating at real time, i.e., a l/l0second rate. Thus, all data which has accumulated during the H10 secondperiod during which the register was loaded, is simultaneously availableat readout time. The unload gates 135 and 136 are also controlled bymemory control logic 130, which also controls the sync and section 1inhibit gates 137 and 138 which in turn control the digital adder 125.The shift register sets each have one register that has a 1 bit indexvalue to mark the start of the 819 bit cycle. This index register actsas a cycle counter. The memories are cleared by the adder during thefirst sector operation because of the presence of the sector 1 inhibitpulse which effectively adds only zero to the new input data.

Referring to FIG. 10, the timing chain and track select system module 14which controls the sweep drive 15 and the highly regulated CRT powersupply 16 is illustrated in greater detail. Track select data from thecontrol computer is supplied by a data buss 141 which feeds through alink 142 to a sector select command register 143. The register 143unloads to a sector select register comparator 144, the output 145 ofwhich ANDs to a gate 146. Track selection data is also fed through alink 147 to a track select command register 148 which unloads to a trackselect register comparator 149, the output of which also ANDs to gate146. Enabled gate 146 is linked by 150 to a multiplexer 151 having asingle line data in and an n" channels out to channel sampling gates152.

Control computer data in the form of output address is carried by a databuss 132 to the multiplexer, whereby the output of selected tracks isgated to correct sample gates governing multiple output channels. Thetrack count state is fed to comparator 149, and the sector counter stateis fed to the comparator 144. Track count state is also fed to thecomputer to synchronize command timing to the track selection data.Thus, where multiple output channels are provided responsive toindividual commands for data related to the multiple output channels, itis possible to respond to each command serially in the order in whichthe required data is reached during a single complete sweep of therecord.

At this point in the disclosure, it is considered advantageous to reviewthe major timing events which occur during operation. The modulationoccurring during the crossing of a single track occurs during a periodof 106.4038067 nanoseconds. During this time, the scanning beamcrosses-one band 74 (FIGS. 4 and one band 75 and arrives at the nextband 74. Each vertical slice (y scan) is divided into 216 virtual trackperiods. The track period frequency is 9.398160 Ml-lz.

During a single slice of the scanning operation, (y sweep) the end ofthe sweep is triggered by the 201st count in the track counter, withphase lock to the timing chain module. This period is derived from the4,351 slices per complete scan. There are 64 start and end slices, 32ineach of the four bands between the five sectors, and 819 in each sector.The slice frequency in scanning is therefore 43.51 KHz.

The scanning of a single sector requires 18.823259 milliseconds 'for'819 slices added to 1470.9262 microseconds for the 64 slices at thestart of the scan. During one complete scan, all sectors are sampled andmemory loaded with data required for output during the next millisecondperiod. Maximum cueing time is therefore less than 100 milliseconds. Ifprior scan occurred in a previous sector, then the contents aresimultaneously clocked out at the real time rate over the 100millisecond period. Real time output is at a 500 millisecond rate, andencompasses the output of five cycles of scan over each of the fivesectors.

I wish it to be understood that I do not consider the invention limitedto the precise details of structure shown and set forth in thisspecification, for obvious modifications will occur to those skilled inthe art to which the invention pertains.

I claim:

1. In a data storage and retrieval system, a data record including atleast one elongated track, scanning means progressively orthogonallyscanning said track and passing a radiant energy beam throughenergytransmissive portions of said track, energy detector meansdisposed on an opposite side of said record, and pulse width modulationmeans receiving the output of said energy detector means; said trackcomprising a first undulating elongated energy-transmissive area, secondand third elongated non-energy-transmissive areas bordering said firstarea, and a fourth rectilinear energy-transmissive area bordering one ofsaid second and third areas; whereby orthogonal scanning of said trackmay create a pulse width modulated signal determined by theinstantaneous orthogonal spacing between said first and fourth elongatedareas.

2. Structure in accordance with claim 1, further characterized in asweep drive means controlling the defiection of said scanning means,track pulse counter means operated by the crossing of a scanning beam ofsaid first mentioned area, timing chain means regulating said sweepdrive, sync comparator means receiving an output from said track pulsecounter means and said timing chain means, and providing a regulatoryoutput signal to said sweep drive.

3. Structure in accordance with claim 1, including transversal filtermeans sensing the leading edge of each radiant energy pulse formed bythe passing of radiant energy beams through each of said first andfourth areas, and employing the detection of the start of the fourtharea to determine pulse width.

1. In a data storage and retrieval system, a data record including atleast one elongated track, scanning means progressively orthogonallyscanning said track and passing a radiant energy beam throughenergy-transmissive portions of said track, energy detector meansdisposed on an opposite side of said record, and pulse width modulationmeans receiving the output of said energy detector means; said trackcomprising a first undulating elongated energy-transmissive area, secondand third elongated non-energy-transmissive areas bordering said firstarea, and a fourth rectilinear energy-transmissive area bordering one ofsaid second and third areas; whereby orthogonal scanning of said trackmay create a pulse width modulated signal determined by theinstantaneous orthogonal spacing between said first and fourth elongatedareas.
 2. Structure in accordance with claim 1, further characterized ina sweep drive means controlling the deflection of said scanning means,track pulse counter means operated by the crossing of a scanning beam ofsaid first mentioned area, timing chain means regulating said sweepdrive, sync comparaTor means receiving an output from said track pulsecounter means and said timing chain means, and providing a regulatoryoutput signal to said sweep drive.
 3. Structure in accordance with claim1, including transversal filter means sensing the leading edge of eachradiant energy pulse formed by the passing of radiant energy beamsthrough each of said first and fourth areas, and employing the detectionof the start of the fourth area to determine pulse width.